1. Feature:Keep your reference tension in check with the tension calibrator stringer tools 2. A must have for proper stringing machine maintenance. 3. A racket that has just been put on or used for a period of time, usually the midpoint value of value measured by the pressure gauge is too small, and the pressure value around to be more pounds, compared to the horizontal line, vertical 's beat value to be more pounds. specification: 1. 0-42lbs 2. Know when it is time to restring 3. Easy to operate 4. Model:AC-SM200 colour: black Material: PVC Package Contents: 1 x Tension Calibrator Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.